U.S. patent application number 09/799842 was filed with the patent office on 2002-09-12 for method and apparatus to encode information in, and dispose a human-readable pattern on, a rotatable data storage medium.
This patent application is currently assigned to International Business Machines Corporation. Invention is credited to Emberty, Robert George, Klein, Craig Anthony.
Application Number | 20020126617 09/799842 |
Document ID | / |
Family ID | 25176904 |
Filed Date | 2002-09-12 |
United States Patent
Application |
20020126617 |
Kind Code |
A1 |
Emberty, Robert George ; et
al. |
September 12, 2002 |
Method and apparatus to encode information in, and dispose a
human-readable pattern on, a rotatable data storage medium
Abstract
A method to store first information in a rotatable data storage
medium and to dispose second information on a rotatable data
storage medium. An apparatus comprising a constant linear velocity
drive servo, a laser device, and a computer useable medium having
computer readable program code disposed therein for sequencing
laser irradiations to encode first information in a rotatable data
storage medium and to dispose second information on a rotatable
data storage medium. A rotatable disk storage medium having first
information encoded in the information area and at least one
human-readable pattern disposed on the clamp area and/or the
information area.
Inventors: |
Emberty, Robert George;
(Tucson, AZ) ; Klein, Craig Anthony; (Tucson,
AZ) |
Correspondence
Address: |
Dale F. Regelman
Hayes, Soloway, Hennessey,
Grossman & Hage, P.C.
130 W. Cushing Street
Tucson
AZ
85701
US
|
Assignee: |
International Business Machines
Corporation
|
Family ID: |
25176904 |
Appl. No.: |
09/799842 |
Filed: |
March 6, 2001 |
Current U.S.
Class: |
720/658 ;
369/275.2; 720/718; G9B/23.006; G9B/23.093; G9B/7.032 |
Current CPC
Class: |
G11B 7/00736 20130101;
G11B 7/24094 20130101; G11B 23/0042 20130101; G11B 23/40
20130101 |
Class at
Publication: |
369/272 ;
369/275.2 |
International
Class: |
G11B 003/70; G11B
005/84; G11B 007/26; G11B 007/24 |
Claims
What is claimed is:
1. A method to store first information in, and to dispose second
information on, a rotatable data storage medium, comprising the
steps of: providing a rotatable data storage medium recording
apparatus; providing a rotatable data storage medium, wherein said
a rotatable data storage disk comprises a clamp area and an
information area; placing said rotatable data storage medium into
said recording apparatus; encoding said first information in said
information area; and disposing said second information on said
rotatable data storage medium.
2. The method of claim 1, wherein said wherein said recording
apparatus comprises a laser device.
3. The method of claim 2, wherein said second information comprises
a human-readable pattern.
4. The method of claim 3, wherein said human-readable pattern is
disposed on said information area.
5. The method of claim 3, wherein said human-readable pattern is
disposed on said clamp area.
6. The method of claim 3, wherein said rotatable data storage
medium comprises an optical disk.
7. The method of claim 6, wherein said optical disk comprises a
writable optical storage disk.
8. The method of claim 6, wherein said optical disk comprises a
re-writable optical storage disk.
9. The method of claim 1, wherein said disposing step further
comprises using a constant angular velocity drive servo.
10. The method of claim 1, wherein said disposing step further
comprises using a constant linear velocity drive servo.
11. The method of claim 10, further comprising the steps of:
determining an initial timing vector required to dispose an initial
portion of said pattern, wherein said initial portion of said
pattern is disposed at an initial radius R.sub.initial; and
determining an incremental timing vector to dispose an incremental
portion of said pattern, wherein said incremental portion of said
pattern is disposed at an incremental radius R.sub.incremental.
12. The method of claim 11, wherein said incremental timing vector
is determined using the equation: incremental timing
vector=(initial timing
vector)(R.sub.incremental/R.sub.initial).
13. The method of claim 12, wherein said initial timing vector
comprises the time of commencing the initial irradiation, the
initial irradiation time period, and the initial period between
irradiations.
14. The method of claim 13, wherein said incremental timing vector
comprises the time of commencing the incremental irradiation, the
incremental irradiation time period, and the incremental period
between irradiations.
15. A rotatable data storage medium recording apparatus to encode
information in a rotatable data storage medium and to dispose a
human-readable pattern on said rotatable data storage medium,
wherein said rotatable data storage medium recording apparatus
comprises a laser device, a constant linear velocity drive servo,
and a computer useable medium having computer readable program code
disposed therein for sequencing irradiations from said laser device
onto said rotatable data storage medium, the computer readable
program code comprising a series of computer readable program steps
to effect: determining an initial timing vector required to dispose
an initial portion of said human-readable pattern on said rotatable
data storage medium, wherein said initial portion of said
human-readable pattern is disposed at an initial radius
R.sub.initial; and determining an incremental timing vector to
dispose an incremental portion of said human-readable pattern on
rotatable data storage medium, wherein said incremental portion of
said human-readable pattern is disposed at an incremental radius
R.sub.incremental.
16. The rotatable data storage medium recording apparatus of claim
15, wherein said rotatable data storage medium comprises an optical
disk.
17. The rotatable data storage medium recording apparatus of claim
16, wherein said optical disk comprises a writable optical storage
disk.
18. The rotatable data storage medium recording apparatus of claim
16, wherein said optical disk comprises a re-writable optical
storage disk.
19. The rotatable data storage medium recording apparatus of claim
13, wherein said computer readable program code further comprises a
series of computer readable program steps to determine said
incremental timing vector using the equation: incremental timing
vector=(initial timing
vector)(R.sub.incremental/R.sub.initial).
20. The rotatable data storage medium recording apparatus of claim
19, wherein said initial timing vector comprises the time of
commencing the initial irradiation, the initial irradiation time
period, and the initial time period between irradiations.
21. The rotatable data storage medium recording apparatus of claim
20, wherein said incremental timing vector comprises the time of
commencing the incremental irradiation, the incremental irradiation
time period, and the incremental time period between
irradiations.
22. A rotatable disk storage medium comprising a clamp area and an
information area wherein first information is encoded in same
information area, and wherein a first human-readable pattern is
disposed on said information area.
23. The rotatable disk storage medium of claim 22, wherein a second
human-readable pattern is disposed on said clamp area.
24. The rotatable disk storage medium of claim 22, wherein said
first human-readable pattern is disposed on said clamp area.
25. The rotatable disk storage medium of claim 22, wherein said
rotatable data storage medium comprises an optical disk.
26. The rotatable disk storage medium of claim 25, wherein said
optical disk comprises a writable optical storage disk.
27. The rotatable disk storage medium of claim 25, wherein said
optical disk comprises a re-writable optical storage disk.
Description
FIELD OF THE INVENTION
[0001] The present invention is generally directed to an
information storage method and apparatus wherein that apparatus and
method allow the same recording device to both write information to
a rotatable data storage medium, and to also dispose a
human-readable pattern on that rotatable data storage medium.
BACKGROUND OF THE INVENTION
[0002] The commercial craving for increased information storage
density on recordable media has been a significant driving force in
present day information-handling systems technology development.
Commercial and market forces have driven the demand for an increase
in the raw amount of data needed to be stored and accessed upon a
removable device. These forces have also increased the demand that
this information be available quickly and accurately. In addition,
there has been an increase in the desire to make the information on
these disks writable by end users.
[0003] In that regard, optical storage media, and more
particularly, the optical disk, is currently finding increasing use
in the high density storage of large quantities of data. In the
optical medium, the information is retrieved through the
interaction of a radiation beam with the information storage
medium. At present, three principal types of optical storage media
are in common use.
[0004] The first type of optical storage medium is manufactured
with the information stored thereon, generally in the form
depressions formed into a polycarbonate substrate. A reflecting
coating is deposited on the polycarbonate substrate and the
radiation beam is focused on the reflecting layer. This type of
optical disk is frequently referred to as a ROM (i.e., read only
memory) disk. Because a ROM disk is not an end user writable disk,
Applicants' method and apparatus are not used in conjunction with
such a ROM disk.
[0005] The second type of optical storage medium has the capability
of having information recorded (written) thereon at some time after
the fabrication of the medium. Such an optical storage medium in
the disk embodiment is frequently referred to as a writable optical
storage disk. In general, information can only be written one time
to such a writable disk. Such disks are sometimes call "write once"
disks. Applicant's apparatus and method can be used to both write
data to the information portion of such a writable disk, and to
dispose a human-readable pattern such as a label on the
non-information portion of that disk.
[0006] The third type of optical storage medium also has the
capacity to have information recorded on the medium after
fabrication. In addition, at a later time, the stored information
can be erased or modified. This type of optical storage medium in
the disk embodiment is generally referred to as an erasable or a
re-writable optical storage disk. Applicant's apparatus and method
can be used to both write data to the information portion of such a
re-writable disk, and to dispose a human-readable pattern such as a
label on the non-information portion of that disk.
[0007] In each type of optical storage (disk) medium, the storage
layer is supported and protected by a polycarbonate support
substrate and by a protective (lacquer) overcoat layer. However,
the storage layer is modified in the writable disk and in the
re-writable disk. The storage layer in the writable disk includes a
reflector layer (generally fabricated from gold) proximate the
lacquer overcoat layer and includes a recording layer, typically a
dye polymer layer, proximate the polycarbonate layer. The newly
fabricated re-writable optical storage disk has a recording layer
that is responsive to radiation having selected parameters, the
radiation changing the optical properties of the recording
layer.
[0008] With either the writable and re-writable disks, differences
in the optical properties of the recording layer can be detected,
through the interaction with an impinging radiation beam and data,
encoded by means of the optical property changes, can be recovered.
The recording, storage, and/or the reflective layer of the
writable/re-writable optical disks are many times called the
storage layer. In the optical information storage and retrieval
system, a read/write head is moved in a specified path relative to
the optical storage medium. The read/write head provides a
radiation beam which, after interacting with a region of the
optical storage medium, is detected. The information stored on the
optical storage medium takes the form of data-bearing regions with
differing optical properties depending, for example on the logical
state being represented by the particular region. The radiation
beam which has interacted with the optical storage medium has
detectable differences resulting from the interaction with the
information-bearing regions. These detectable differences are
converted into electrical signals. The electrical signals are
subsequently converted to a format which can be conveniently
manipulated by a signal processing system.
[0009] In each of the disk embodiments described above, the
information stored on the disk may be considered to lie in a series
of tracks spaced radially from a center hub, sometimes called the
clamp area. The information track typically begins in a pre-user
data area near the center hub. A user-data area follows the
pre-user data area, and contains the information imparted to the
disc. A lead-out area follows the user-data area, lying closer to
the outer edge of the disc. The lead-out area generally contains no
user data. The pre-user data area, user-data area, and lead-out
area collectively comprise the "information area" of the disc.
[0010] As the spiral information track progress from the center
area to the outer edge area, the radius of that track gradually
increases. Thus, the information content is encoded in the
information area in a slightly arcuate, circumferential
pattern.
SUMMARY OF THE INVENTION
[0011] Applicants' invention includes an apparatus to encode first
information in, and dispose second information on, a rotatable data
storage medium. Such first information may comprise, for example,
data stored in the information area of an optical disk. Such second
information may comprise, for example, one or more human-readable
patterns disposed on the clamp area of an optical disk and/or
disposed in the information area of that disk.
[0012] Applicants' apparatus includes a rotatable data storage disk
recording apparatus having a constant linear velocity ("CLV") drive
servo. A rotatable data storage disk which includes a clamp area
and a information area is placed in Applicants' apparatus, and that
apparatus encodes both first information and second information
within, for example, the information area of the disk.
[0013] Applicants' invention further includes a method to encode
first information in, and dispose second information on, a
rotatable data storage medium, using a recording apparatus having a
CLV drive servo. Applicant's method involves scaling the timing
vectors used by such a CLV apparatus to, for example, radially
dispose a human-readable pattern on either the information area
and/or the clamp area of an optical disk.
[0014] Applicants' invention further comprises a rotatable disk
storage medium having a clamp area and an information area, where
that rotatable medium has first information encoded in the
information area and one or more human-readable patterns disposed
on the information area and/or the clamp area. In certain
embodiments, Applicants' rotatable disk storage medium comprises an
optical disk.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The invention will be better understood from a reading of
the following detailed description taken in conjunction with the
drawings in which like reference designators are used to designate
like elements, and in which:
[0016] FIG. 1 is a top view showing the portions of a typical
rotatable data storage medium;
[0017] FIG. 2 shows a human-readable, radially-oriented,
rectangular pattern disposed on a rotatable data storage
medium;
[0018] FIG. 3 shows an offset pattern formed using a fixed timing
scenario with a recording apparatus having a CLV disk servo;
[0019] FIG. 4 shows the initial radius and incremental radii for
the various portions of the offset pattern of FIG. 3;
[0020] FIG. 5 shows a human-readable, radially-oriented,
rectangular pattern formed using Applicants' method in conjunction
with a recording apparatus having a CLV disk servo; and
[0021] FIG. 6 graphically depicts a fixed timing sequence used by
prior art CLV recording devices.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] Turning to FIG. 1, optical data storage disk 100 comprises
four regions which, with increasing radius can be defined as the
following. Aperture 110 provides a structure to engage a spindle
for controlled rotation of disk 100. The next area is clamp area
120.
[0023] Clamp area 120 typically does not have a data storage layer
associated therewith. Rather, clamp area 120 is used to provide a
space wherein the spindle can be mechanically coupled to the disk
without interfering with access to the data stored on the disk.
[0024] Mirror area 130 has a data storage layer associated
therewith but typically does not have information embedded therein.
Therefore, mirror area 130 typically has a mirror-like appearance.
Information area 140 includes a data information storage layer
associated therewith, and therefore, has data stored therein.
Consequently, because of the structure comprising data embedded
within the data storage layer, information area 140 typically has a
dull appearance when compared to the mirror-like appearance of
mirror area 130.
[0025] Applicants' invention includes an apparatus and a method for
writing data on information area 140 by using a recording device,
such as a laser, and for using that same device to dispose one or
more human readable patterns comprising text and/or graphics, such
as a label, on the information area 140, the clamp area 120, or
both. Recording data on the information area of such a
writable/re-writable disk occurs when a laser light amount per unit
area irradiated exceeds a predetermined value. Disposing a
human-readable pattern on the clamp area occurs when, for example,
sufficient laser energy is directed to specific portions of the
surface of the molded plastic disk to carbonize those surface
portions. Disposing a human-readable pattern on the information
area occurs when the laser device irradiates portions of the
information area thereby altering the optical properties of those
irradiated portions such that the irradiated portions reflect light
in the visible spectrum differently than do the non-irradiated
areas of the information area.
[0026] Disk drive systems for recording and/or reproducing data on
and/or from such a rotatable data storage disk utilize either a
constant angular velocity ("CAV") drive servo or a constant linear
velocity ("CLV") drive servo. Using a CAV drive system, data is
recorded and/or reproduced on and/or from the disk such that the
rotation rate of the disk is kept constant. On the other hand when
using a CLV drive system, data is recorded and/or reproduced data
on and/or from the disk such that the linear velocity of the disk
is kept constant.
[0027] When recording on a disk with a diameter of 20 cm using the
CAV drive mode, the rotation rate of the disk is constant at about
900 revolutions/minute (r.p.m.). In contrast, in the CLV drive mode
the linear velocity is kept constant, and therefore, the disk is
rotated at about 900 r.p.m. at its inner periphery. As the optical
recording device or head is moved toward the outer periphery of the
disk, however, the revolution number of the disk is lowered and the
disk is rotated at about 525 r.p.m. in its outer periphery.
[0028] Optical disk media, including writable and re-writable
disks, is generally written and read at a constant linear velocity.
Thus, optical disk recording devices generally use a CLV drive
servo. This differs from the typical hard-disk drive media and
high-density floppy-disk drive media, which are written to, and are
read from, using a constant angular velocity.
[0029] In order to dispose a human-readable pattern on a disk using
a recording apparatus having a CAV servo, the laser pulses are
simply timed from a revolution index mark. As discussed above,
however, optical disk recording drives exclusively utilize a CLV
servo mechanism. Moreover, these drives typically do not have a CAV
servo.
[0030] Therefore, when using a recording apparatus having only a
CLV drive servo, the fixed timing scheme used with a CAV drive
servo must be modified. Disposing a radially-oriented, human
readable pattern onto a rotatable data storage medium necessarily
means that a change in the radius will occur with respect to the
initial portions of the pattern in relation to the final portion of
the pattern. Referring to FIG. 2, pattern 200 is radially disposed
on the clamp area of an optical disk, with first edge 210 disposed
nearest the aperture and second edge 220 disposed farthest from the
aperture. The radius from the center of the aperture to first edge
210 is necessarily shorter than the radius from the center of the
aperture to second edge 220.
[0031] Because of the change in radius while radially disposing
pattern 200 onto a rotating disk, a CLV drive servo alters the
speed of the disk while disposing that pattern in order to maintain
a constant media velocity under the laser head. Therefore, the
timing scheme used for disposing a pattern, such as a label, onto a
rotating disk using a CAV servo drive must be adjusted, or scaled,
to account for the change in speed of the media. This scaling
factor is directly related to the change of radius encountered
while writing such a large pattern to the media.
[0032] Referring again to FIG. 2, rectangular graphic 200 is
approximately 2 mm high. Referring to Equation (1), it is axiomatic
that the circumference of circle equals twice the radius times
pi.
C=(2)(.pi.)(R) (1)
[0033] where C is circumference and R is the radius. Thus, the
change in the circumference upon a change in the radius is shown in
Equation 2.
.DELTA.C=(2)(.pi.).DELTA.(R) (2)
[0034] Therefore, if there is a .DELTA.R during the writing of a
pattern, such as a label, on a medium rotated using a CLV drive,
there will be a corresponding .DELTA.C offset of the pattern.
[0035] Referring to FIG. 3, graphic 300 was disposed on a rotating
disk using a recording apparatus having a CLV drive and a timing
pattern wherein the recording laser device is turned on and then
off at fixed intervals. Graphic 300 was formed during five (5)
rotations, and comprises initial portion 310, first incremental
portion 320, second incremental portion 330, third incremental
portion 340, and fourth incremental portion 350.
[0036] In using a CLV drive servo and fixed timing intervals,
initial portion 310 is formed by initiating irradiation of the
surface of the disk at time T.sub.0on to form first edge 314. The
surface irradiation continues until time T.sub.0off. The cessation
of irradiation forms second edge 316. Therefore, in order to form
initial portion 310 the laser recording device was operated for a
time period .DELTA.T.sub.0on corresponding to T.sub.0off-T.sub.0on.
FIG. 6 graphically depicts the time segments wherein the recording
device is "on" and wherein the recording device is "off." After
forming initial portion 310, no further surface irradiation occurs
until the disk completes almost a complete rotation. As shown in
FIG. 6, no irradiation takes place during the period of time
corresponding to .DELTA.T.sub.0off.
[0037] Subsequently, first incremental portion 320 is formed by
again irradiating the disk surface, beginning at time T.sub.1on,
and continuing that irradiation for time .DELTA.T.sub.1, where
.DELTA.T.sub.0=.DELTA.T.s- ub.1. No irradiation then occurs for a
period of time corresponding to .DELTA.T.sub.1off. Second
incremental portion 330 is formed once again beginning irradiation
at time T.sub.2on, and continuing that irradiation for time
.DELTA.T.sub.2, where .DELTA.T.sub.0=.DELTA.T.sub.1=.DELTA.T.sub-
.2. In this fixed timing scenario, the periods when no irradiation
occurs, namely .DELTA.T.sub.0off and .DELTA.T.sub.1off, are
equal.
[0038] Referring again to FIG. 3, first incremental portion 320 is
offset from initial portion 310 by distance D.sub.1. The distance
D.sub.1 corresponds to the .DELTA.C offset discussed above. Again
referring to FIG. 3, each subsequent incremental portion is offset
from the previous portion. Distance D.sub.2 represents the
aggregate offset error resulting from using a fixed timing scheme
and a CLV servo mechanism when radially disposing a human readable
pattern, such as a label, on a rotatable disk. When writing a label
having a radial height of 2 mm, the offset error would be as great
as (2)(.pi.)(2 mm), or greater than 12 mm in the tangential
direction. This offset error is not a function of the original
radius of the pattern, but is solely a function of the change of
radius encountered as the total pattern is written.
[0039] Thus, if a fixed timing scheme is used for CLV recording,
there will always be a slewing of the pattern. For recording over a
partial revolution of .THETA. radians, the error is given by
equation (3).
.DELTA.ARC=(.THETA.)(.DELTA.R) (3)
[0040] Thus, a fixed timing scheme cannot be used with a recording
device having a CLV servo to radially dispose a human readable
pattern, such as a label, on a rotatable disk, such as an
writable/re-writable optical disk. Therefore, Applicants' method
uses Equation (4) to scale the timings for sequential irradiations
to form incremental portions of a human-readable pattern based upon
the ratio of the incremental radius to the initial radius.
Incremental Timing Vector=(Initial Timing
Vector)(R.sub.incremental/R.sub.- initial) (4)
[0041] By initial timing vector, Applicants mean, with respect to
forming first incremental portion 320, the time of commencing the
initial irradiation T.sub.0on, the initial irradiation time period
.DELTA.T.sub.0on, and the initial period between irradiations
.DELTA.T.sub.0off. By incremental timing vector, Applicants mean in
this example, the time of commencing the first incremental
irradiation T.sub.1on, the first incremental irradiation time
period .DELTA.T.sub.1, and the first incremental time period
between irradiations .DELTA.T.sub.1off. Referring to FIG. 4, by
R.sub.initial Applicants mean, in this example, the distance
R.sub.0 from the center of aperture 110 (FIG. 1) to bottom edge 312
of initial portion 310. By R.sub.incremental Applicants mean
distance R1 from the center of aperture 110 (FIG. 1) to bottom edge
322 of first incremental portion 320.
[0042] When disposing second incremental portion 330, the initial
timing vector means time T.sub.1on, time period .DELTA.T.sub.1on,
and time period .DELTA.T.sub.1off, and the incremental timing
vector means time T.sub.2on, .DELTA.T.sub.2on, and
.DELTA.T.sub.2off. Similarly in conjunction with disposing second
incremental portion 330, R.sub.initial means the distance R.sub.1
from the center of aperture 110 (FIG. 1) to bottom edge 322 of
first incremental portion 320, and R.sub.incremental means distance
R2 from the center of aperture 110 (FIG. 1) to bottom edge 332 of
second incremental portion 330.
[0043] In a similar fashion, radii R3 and R4 are used to scale the
timing vectors to form third incremental portion 340 and fourth
incremental portion 350, respectively. When properly scaling each
incremental timing vector, the recording apparatus using a CLV
drive servo disposes on a rotatable disk the pattern shown in FIG.
5.
[0044] Graphic 400 is formed from initial portion 410, first
incremental portion 420, second incremental portion 430, third
incremental portion 440, and fourth incremental portion 450. By
scaling the timing vectors used to form these individual portions,
each incremental portion is properly aligned with the portion below
it and also with the portion above it.
[0045] Applicants' recording apparatus includes a constant linear
velocity drive servo, a laser recording device, and a computer
useable medium having computer readable program code disposed
therein for sequencing laser irradiations to encode first
information in a rotatable data storage medium and to dispose
second information on a rotatable data storage medium.
Specifically, the computer readable program code comprises a series
of computer readable program steps to first determine an initial
timing vector required to dispose an initial portion of a
human-readable pattern on the rotatable data storage medium, where
that initial portion of said human-readable pattern is disposed at
an initial radius R.sub.initial. Referring to FIG. 4, R.sub.initial
comprises, for example, radius R0 which represents the distance
from the center of the hub to side 213 of initial portion 310.
[0046] The computer readable program code disposed in Applicants'
apparatus further includes a series of computer readable program
steps to determine an incremental timing vector to dispose an
incremental portion of the human-readable pattern on rotatable data
storage medium, where that incremental portion of said
human-readable pattern is disposed at an incremental radius
R.sub.incremental. Referring again to FIG. 4, R.sub.incremental
comprises, for example, R1 which represents the distance from the
center of the hub to side 322 of first incremental portion 320. The
computer readable program code disposed in Applicants' apparatus
further includes a series of computer readable program steps to
determine the incremental timing vector using the equation:
incremental timing vector=(initial timing
vector)(R.sub.incremental/R.sub.- initial)
[0047] where the initial timing vector comprises the time of
commencing the initial irradiation, the initial irradiation time
period, and the initial time period between irradiations, and where
the incremental timing vector comprises the time of commencing the
incremental irradiation, the incremental irradiation time period,
and the incremental time period between irradiations.
[0048] While the invention has been described in detail herein in
accordance with certain preferred embodiments thereof, many
modifications and changes therein my be effected by those skilled
in the art. Accordingly, it is intended by the appended claims to
cover all such modifications and changes as fall within the true
spirit and scope of the invention.
* * * * *